This invention relates to a process for the production of enzymatically active biocatalysts which re insoluble in aqueous media and which are particularly suitable for use in fluidised-bed or fixed-bed reactors.
The carrying out of enzymatic reactions on an industrial scale has resulted in the appearance of biocatalysts which are insoluble in aqueous media. The reason for this is that the enzymes should not be deactivated after being used only once, which has resulted in their being fixed to an inert support or in their "immobilisation" to enable them to be physically separated from the substance to be treated or "substrate".
Several methods for fixing enzymes to supports have been proposed:
The enzyme is directly adsorbed onto a mineral material, such as ceramics, glass, silica, etc. The products obtained have the disadvantage of being unstable because the enzyme is only weakly fixed to the support.
The enzyme is chemically bound to an organic support, such as a synthetic polymer (for example an aminoethyl cellulose according to British Patent No. 1,357,317) or a natural polymer (for example chitosan according to U.S. Pat. No. 4,094,743) by way of a bifunctional reagent, such as a dialdehyde, or a monofunctional reagent, such as a carbodiimide. The enzymes immobilised on a synthetic support do not have the requisite quality for use in foods. On the other hand, organic supports are not really suited to industrial processes because they are compressible and have a relatively low density and, because of this, they are difficult if not impossible to use in highthroughput fluidised-bed or fixed-bed reactors.
In addition, it is necessary to ensure good contact between the enzyme and the substance to be converted, i.e. the substrate. This means that the enzyme is preferably immobilised on the outer surface and not in the pores or in the matrix of the inert support.
The above-mentioned difficulties and restrictions affecting practical application are more severe if the reaction medium is viscous and contains colloidal or solid substances or impurities. Difficulties such as these are currently being encountered in the food industry.